Researchers are encouraged by the numbers, but they say more studies and data need to be collected to get a better understanding of the impact of legal marijuana on teenagers.

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Cannabis use by teenagers in Washington has dropped since the drug was legalized in 2012, according to a study published Wednesday by the Journal of the American Medical Association.

The study comprised two years of data, from 2014-2016, and showed decreases in marijuana usage by teens in middle- and high school. Use among 8th graders dropped from 9.8 to 7.3 percent over that period and among 10th graders, use fell from 19.8 to 17.8 percent. Use by seniors remained flat at just over one in four students, 26.7 percent, during that period, according the study.

Legal age to consume marijuana in Washington is 21.

There was concern when the drug was legalized that use among youngsters would skyrocket, so researchers are finding the numbers encouraging, said Julia Dilley, one of the study’s authors and a senior research scientist/epidemiologist at the Oregon Health Authority and Multnomah County Health Department. She cautioned, however, that the data is limited and there is much to learn about the impacts of legalization on adolescents.

“Rather than try and draw conclusions immediately, we need to keep looking at youth and different types of youths, and communities,” she said. “It’s just far too soon to say what the impact of legalization is on youth.”

The study, which was published Wednesday in JAMA Pediatrics, was a joint effort from researchers at the RAND Corporation and other organizations including the Washington State Liquor and Cannabis Board. The study used data collected by the Washington Healthy Youth Survey, an anonymous survey given every two years to 8th, 10th and 12th-graders.

Mary Segawa, public health-education liaison at the Washington State Liquor and Cannabis Board, and one of the study’s authors, stressed that additional studies and data are needed to get a clear picture of how legal cannabis is impacting youth. She said public-health officials were holding their breath after Washington voters approved legalization, but one of the positives has been the open dialogue about marijuana use with adolescents.

“After legalization there was a lot of concern about what this would do for youth use,” Segawa said. “One of the things legalization did was start conversations.”

Segawa said researchers aren’t able to pinpoint the reasons why usage has dropped. She said the Liquor and Cannabis Board, and other agencies like the state Department of Health, are going to continue collecting data through the Healthy Youth Survey and get a more refined picture of how cannabis is impacting teenagers in general and how groups are affected.

More study is needed on the issue before researchers will be able to understand the trends surrounding young people and marijuana, said Rosalie Liccardo Pacula, co-author of the study and co-director of the RAND Drug Policy Research Center.

“These findings do not provide a final answer about how legalization ultimately may influence youth marijuana usage. A variety of factors may influence the behavior of adolescents and those factors are likely to influence behaviors in different ways over time,” Pacula said.

A similar study in Colorado, which also legalized cannabis in 2012, found that marijuana use by teenagers has stayed essentially flat, going from 20 percent saying they had used in 2013 to 19 percent in 2017.